Webtask compilers for Auth0 platform extensibility points
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README.md

This repository contains webtask compilers that enable custom programming models for Auth0 platform extensibility points.

This module is installed on the webtask platform via the webtask-mongo docker image.

Creating Auth0 extensions with wt-cli

To create a webtask that implements a specific extensibility point, you can use the wt-cli tool or a corresponding webtask API call. For example, to create a client-credentials-exchange extension you could call:

cat > custom_claims.js <<EOF
module.exports = function(client, scope, audience, context, cb) {
  var access_token = {};
  access_token['https://foo.com/claim'] = 'bar';  
  access_token.scope = scope;
  access_token.scope.push('extra');
  cb(null, access_token);  
};
EOF

SECRET=$(openssl rand 32 -base64) && \
wt create custom_claims.js \
    -p default-tjanczuk \
    --meta wt-compiler=auth0-ext-compilers/client-credentials-exchange \
    --meta auth0-extension=runtime \
    --meta auth0-extension-name=credentials-exchange \
    --meta auth0-extension-secret=$SECRET \
    --secret auth0-extension-secret=$SECRET

What is an Auth0 extension

An Auth0 extension is a webtask created in the Auth0 tenant's webtask container and associated with specific metadata properties as outlined in the table below.

Name Required? Value
auth0-extension Yes Must be set to runtime.
auth0-extension-name Yes The name of the extensibility point in Auth0. This is used by Auth0 to select the set of webtasks to run in a specific place and circumstances of Auth0 processing. Available Extensibility Points
auth0-extension-client No Auth0 extension points which only wish to execute extensions configured for a particular client_id will use this value to select the webtasks that should be run.
auth0-extension-disabled No If set, disables the webtask.
auth0-extension-order No Webtasks selected to run for a given extension point in Auth0 will be sorted following an increasing order of this numeric metadata property. If not specified, 0 is assumed. Order of webtasks with the same value of auth0-extension-order is indeterministic.
auth0-extension-secret No Used to authorize calls from Auth0 to Webtasks. See below.

Authorization

Auth0 extensions are executed by issuing an HTTP POST request to the webtask URL from the Auth0 runtime. To ensure that only the Auth0 runtime and/or a specific Auth0 tenant can issue such requests, the requests use a secret-based authorization mechanism. If an extension webtask has been created with the auth0-extension-secret secret parameter, the value of that parameter MUST equal to the value of the Authorization: Bearer {secret} header of the HTTP POST request. To allow the Auth0 runtime to add the necessary header to the webtask request it is making, the same secret value is stored in the auth0-extension-secret metadata property. This setup can be achieved with the following:

SECRET=$(openssl rand 32 -base64) && \
wt create {file}.js \
    --meta wt-compiler=auth0-ext-compilers/{specific-compiler} \
    --meta auth0-extension-secret=$SECRET \
    --secret auth0-extension-secret=$SECRET \
    ...

The authorization check is implemented as part of the webtask compiler for a specific extensibility point - see next section.

Custom programming models

Different Auth0 extensibility points may present unique programming models to the end user with the use of webtask compilers. Webtask compilers for Auth0 extensibility points are implemented as part of this repository which is installed as a Node.js module in the webtask environment. This allows the use of wt-compiler metadata property to select a specific compiler, e.g. with:

wt create {file}.js \
    --meta wt-compiler=auth0-ext-compilers/client-credentials-exchange \
    ...

Webtask compilers for Auth0 extension points also enforce the authorization check described in the previous section.

Extensibility points available

  1. The client-credentials-exchange extensibility point
  2. The pre-user-registration extensibility point
  3. The post-user-registration extensibility point

The generic programming model for all extensibility points

A generic compiler is provided (auth0-ext-compilers/generic) that does not adhere to any extension-specific programming model. Instead, this compiler is a light facade on top of the 2ary and 3ary webtask programming models. The compiler provides authorization of the incoming webtask request and then invokes the supplied function.

2ary generic extension

module.exports = function(ctx, cb) {
  var scope = ctx.body.scope;
  var access_token = {};
  access_token['https://foo.com/claim'] = 'bar';  
  access_token.scope = scope;
  access_token.scope.push('extra');
  cb(null, access_token);  
};

3ary generic extension

module.exports = function(ctx, req, res) {
  var scope = ctx.body.scope;
  var access_token = {};
  access_token['https://foo.com/claim'] = 'bar';  
  access_token.scope = scope;
  access_token.scope.push('extra');
  
  res.writeHead(200, { 'Content-Type': 'application/json' });
  res.end(JSON.stringify(access_token));
};